THE BUTTERFLY. 



tion of these muscles and the squeezing of the sac 

 by the muscles which encircle it, the fluids, pre- 

 vented by the valve from retreating the way they 

 came, are forced down the alimentary canal. 



The only part of the head of which we have not 

 spoken is the labium and its appendages ; in the 



FIG. 70. Longitudinal section of head of Danais Plexippus to show the 

 pharyngeal sac ; mx, left maxilla, the right being removed ; wfl, floor of the 

 mouth cavity or sac ; oe, oesophagus ; ov, oral valve ; srf, salivary duct ; dm 

 and //ft, dorsal and frontal muscles which open the sac ; the cut ends of the 

 transversely encircling muscles are seen above the sac, X 20 (Burgess). 



larva these consisted of the spinneret, and on 

 either side of it a minute jointed palpus like that 

 of the maxillae. In the butterfly, the spinneret 

 is gone, but the palpi have become developed into 

 a three-jointed organ, often of considerable size, 

 with inflated joints, all profusely clothed with 



